The present invention relates to the continuous production and preheating of a hydrocarbon-water vapor or steam blend and mixture to be used as a charge in a reforming process ultimately for the production either of hydrogen or of synthetic gas, being the reform product. Moreover, the invention relates to the construction of a particular heat exchanger for purposes of carrying out this method.
It is known generally to produce hydrogen or a synthetic gas rich in hydrogen in a reformer reactor which includes a suitable catalyst and under utilization of a mixture of hydrocarbon such as methane and water vapor. The hydrocarbon-water vapor blend is heated to a temperature of about 400 to 500 degrees C. and pressurized up to 40 bar and in that stage fed to the reactor. The temperature of that change is increased in the reactor to 750-900 degrees C., depending on the pressure, and now for instance hydrogen gas is produced. The particular reaction carried out in the reactor is endothermic and thus requires a supply of thermal energy. In the case of methane as the hydrocarbon the following equation obtains: EQU CH.sub.4 =H.sub.2 O.revreaction.CO+3H.sub.2
The hydrogen content depends on the excess of the water vapor that is fed into the system as part of the blend or mixture but also on the temperature and pressure in the reforming reactor. If the water vapor excess increases and if the temperature increases the gain in hydrogen is likewise increased while on the other hand an increase in pressure reduces the hydrogen production under otherwise similar circumstances. Depending on the reaction conditions and the excess in water vapor one therefore obtains a hydrogen rich gas which however includes in addition CO and CO.sub.2 possibly also excess water that has not reacted and a certain residue of not reacting methane. This amount of residue generally is again larger the higher the pressure and lower the reforming temperature.
The industrial production of hydrogen and synthetic gas is usually carried as a reaction in vertically arranged pipes or tubes which contain the catalyst and which dip into the radiation zone of the furnace. Owing to the high reforming temperature the thermal efficiency in that radiation zone is quite low. One uses approximately 45 to 60% of the thermal energy that is produced by combustion in the furnace. Assuming that the CO production is not of any interest one can provide for a supplementary reaction in a downstream reactor under utilization of a different catalyst and in accordance with the reaction equation: EQU CO+H.sub.2 O.revreaction.CO.sub.2 +H.sub.2
Owing to this reaction further excess water is used while on the other hand the gain in production is indeed increased. This particular reaction is an exothermic one, and the equilibrium condition is quite independent from pressure. The degree of completeness of the conversion of CO from H.sub.2 and CO.sub.2 increases with a decrease in the conversion temperature. Depending on the catalyst used the conversion temperature is about 350.degree.-450.degree. C. or from 200.degree.-250.degree.. Accordingly the reforming product has to be cooled down prior to the CO conversion to a temperature of about 350.degree. or 200.degree. C. It follows from the foregoing that the heat content in the combustion gases of the furnace as well as in the reforming product is quite high, owing to the low thermal efficiency of the device. The same is true with regard to the amount of heat that is produced during the CO conversion. These combined heat values exceed the requirement for the production of steam as well as for the preheating of the charge of the reformer being the hydrocarbon; the charge water vapor mixture. In order to avoid loss of this excess in heat content it is used, if the equipment so permits, to produce an additional amount of steam which is then discharged in one form or another from the equipment. Such a supplemental steam production and discharge is of course meaningful only if there is a consumer and user for that steam. If not then a recent development comes into play, namely a regeneration reformer was available in which a part of the heat content in the reformed product is used directly in the reformer reaction. That in turn permits some reduction in the amount of heat which remains unused in the radiation zone.
It can readily be seen that claiming and regaining of heat in the reforming device is a multilevel complex problem. It covers broadly the preheating of the hydrocarbons, the production and superheating of steam and the preheating of the hydrocarbon-water vapor mixture. These multiple requirements entail the utilization of separate heat exchanger types which are interconnected for tubing for conduction of the various fluids heating and media to be heated. All this is very expensive.